The present invention generally concerns a system for detecting polynucleotide hybridization. More particularly, the invention pertains to a system for detecting polynucleotide hybridization utilizing piezoelectric crystals. The invention has particular application to medical diagnosis, bacteriology, virology, pathology, and biochemical and molecular biological research. For example, the system of the present invention is useful for detecting polynucleotide hybridizations such as DNA-RNA, DNA--DNA and RNA--RNA hybridizations.
DNA and RNA are strands of nucleic acids characterized by a phosphodiester link between the 3' position of one nucleic acid residue with the 5' position of the next nucleic acid residue. Nucleic acids contain one or more of the following bases: guanine (G), cytosine (C), adenine (A), and either thymine (T) (occurring in DNA) or uracil (U) (occurring in RNA).
In double-stranded DNA it is known that the pairing of the DNA strands are complementary, i.e., the guanine of one strand always pairs with the cytosine of the other strand (G-C), and the adenine of one strand always pairs with the thymine of the other strand (A-T). The same is true for double stranded RNA with the exception that uracil is substituted for thymine (A-U).
Pairing of single strands of polynucleotides occurs through hydrogen bonds formed between complementary bases of the nucleic acids. When heated sufficiently, the paired polynucleotides will melt; i.e., the hydrogen bonds are disrupted and the double strands are separated into individual strands (denatured). The polynucleotide strands tend to re-form duplexes once separated into single strands through the re-forming of hydrogen bonds between complementary bases.
The ability of DNA or RNA strands to reanneal with complementary strands of polynucleotides has led to the ability to determine base sequence homology through hybridization. The extent of hybridization between a DNA strand with a known base sequence, for example, and a strand of polynucleotide from a different source, can serve as a measure of species relatedness, and is useful for the purpose, among others, of identifying bacteria and viruses.
Several methods of detecting polynucleotide hybridization have been developed. One such method of detecting polynucleotide hybridization relies on radiolabeling. Other known methods make use of renaturation rates, electron microscopic determination, and the use of fluorochrome labeled polynucleotides in conjunction with fluorescence microscopy. IgG specific for RNA:DNA hybrids has also been used. Still other methods use nucleotide derivatives which contain biotin, aminobiotin, lipoic acid and other determinants attached covalently to the pyrimidine or purine ring.
The techniques employed for detecting DNA or RNA relatedness have been applied in research laboratories for several purposes, such as identifying biochemically atypical strains, classifying poorly studied groups of organisms, justifying or invalidating proposed taxonomic changes, determining the relationships between newly described organisms and existing taxons, and for identifying mixed cultures. Unfortunately, the application of these techniques in clinical studies have for most purposes been impractical. For example, in clinical studies where DNA hybridization detection employs radiolabeling, the technique has been shown to be impractical since it lacks simplicity and rapidity, is expensive, and poses potential safety hazards.